1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive microactuator and a manufacturing method thereof. In particular, the present invention relates to a piezoelectric/electrostrictive microactuator using a mixture of ceramic powder and polyvinylidene fluoride and a manufacturing method thereof.
2. Description of the Prior Art
An ink jet printer head actuator using a piezoelectric substance is usually composed of an infrastructure made of a vibration plate and a chamber, a piezoelectric substance which undergoes mechanical deformation if electricity is applied is connected on the vibration plate, and electrode(s) which transmit(s) electricity to the piezoelectric substance.
The piezoelectric substance of an actuator has characteristics of poling by which a directionality is given the piezoelectric substance when an electric field is applied. If electricity is supplied to an upper and a lower electrode formed on and under the piezoelectric substance under the poling state, the piezoelectric substance located between the electrodes undergoes mechanical deformation or vibrates with recycling of deformation and restoration.
In the ink jet printer head, ink is sprayed onto a record medium as the vibration plate undergoes mechanical deformation, in thickness, if the piezoelectric substance of the actuator vibrates.
Hitherto a ceramic powder manufactured by a solid phase process has been used to manufacture a piezoelectric/electrostrictive film used as the piezoelectric substance in the piezoelectric/electrostrictive actuator.
The solid phase process, also called oxide process, manufactures the ceramic powder by mixing a raw material containing powder oxides or molten salts to thermally treat it at 1000-1200.degree. C., to pulverize it, and then to sinter it.
Ceramic powder manufactured by such a solid phase process has a disadvantage in that the generated particle size, which is as large as 0.2-2 .mu.m, varies in raw material powder size and in that it needs high temperature heat treatment over 1000.degree. C., according to the process characteristics.
In manufacturing various film types of device using the ceramics, heretofore the process has mainly been used to prepare ceramic paste using a ceramic powder to print it on the vibration plate or to fill it in a mold to thermally treat it.
To prepare ceramic paste traditionally, ceramic grains have been added, with an average particle diameter above I .mu.m manufactured by a solid phase process, into a solution where binder, vehicle, plasticizer, dispersant etc. are dissolved in solvent, then to mix and agitate it.
In order to manufacture a piezoelectric/electrostrictive film using the ceramic paste prepared by the method, the paste is printed on a vibration plate to be dried at 130.degree. C. and thermally treated above 1000.degree. C. A problem is encountered, in that a separate additional heat treatment is needed above 500.degree. C. for binder removal work to completely remove the added organic material component, before the heat treatment after drying.
And there is another problem that the vibration plate is limited to materials which can endure heat treatment above 1000.degree. C., because the ceramic paste prepared by the method cannot be molded at low temperatures so it must be thermally treated above 1000.degree. C.
Also there is a problem in that diverse applications are limited, as the material has no plasticity at all.
Here, a technique is needed to impart flexibility to the ceramic device, without affecting piezoelectric characteristics for sake of permitting diverse applications of the piezoelectric/electrostrictive ceramic device.
Polyvinylidene fluoride {PVDF} is a typical raw material used for preparation of complex substances and widely applied in molding electrodes of a secondary battery PVDF is a polymer having piezoelectric characteristics, which is utilized so that products using the characteristics of PVDF itself are marketed.
But there is problem that its piezoelectric characteristics are lower than that of ceramic powder although it is very moldable.
Thus, a method has been developed to manufacture a ceramic device by mixing the ceramic powder (excellent in piezoelectric characteristics) and the PVDF (excellent in moldability).
In the process the mixture is obtained by placing piezoelectric/electrostrictive ceramic powder, PVDF and a small quantity of binder into an organic solvent of toluene, hexanol etc., then uniformly mixing it by agitating or refluxing, and finally by uniformly mixing it by agitating or refluxing, and finally by vaporizing the solvent and drying the product.
The mixture obtained is processed into a thick film type by rolling process, wherein the thickness of the thick film is determined according to the mixture processibility and the rolling condition.
Differences arise in processibility according to mixing ratio of ceramic powder and PVDF. If PVDF content is increased, processibility is enhanced, but a loss of piezoelectric properties is accompanied by the decrease of ceramic powder content; while if PVDF content is decreased, piezoelectric properties are enhanced at the expense of processibility.
The thick film is made into a device through processes of poling, after electrode treatment, according to the application objective.
In mixing the ceramic powder and the PVDF, minimalization of voids is desireable for uniform mixing, which should be attained to enhance the mechanical properties of the formed film.
Finer ceramic powder use is preferable to minimize voids in a mixture of a definite content ratio of ceramic powder and PVDF.
But there is a problem in traditional ceramic powder that it is difficult to mix it effectively, as particle size is large, as explained above.
Also there is problem in that usable vibration plate range is restricted because a high temperature heat treatment over 1000.degree. C. is necessary, according to ceramic powder characteristics.